Lecture Topic: Evolutionary history of earth

• Concept of Era's : evolutionary history divided into eras.

– Pre-Darwinian concept, credited to Greeks and Egyptians

– Era = A period of time marked by a distinctive character

– Earth's age ~ 4.5 bybp

Figure: Some major episodes in the history of life

Eukaryote versus Prokaryote

• Prokaryotes are organisms, such as bacteria that lack nuclei and other complex cell structures. Eukaryotes share a common origin, and are broken into archea (ancient) and true bacteria. The name comes from the Greek, ευ, meaning good, and κάρυον, meaning nut, in reference to the cell nucleus.

Eukaryote versus Prokaryote

• Eukaryotes are organisms with complex cell/s in which the genetic material is organized into membrane bound nuclei and other organelles.

• Eukaryotes (also spelled "eucaryotes") comprise protista (unicellular) and animals, plants and fungi (multi-cellular).

Prokaryotes and Eukaryotes

The major similarities between the two types of cells (prokaryote and eukaryote) are:

1.They both have DNA as their genetic material.

2.They are both membrane bound.

3.They both have ribosomes.

4.They have similar basic metabolism.

5.They are both amazingly diverse in forms.

Major differences between Prokaryotes and Eukaryotes

• The major and extremely significant difference between prokaryotes and eukaryotes is that eukaryotes have a nucleus and membrane-bound organelles, while prokaryotes do not.

• The DNA of prokaryotes floats freely around the cell.

• The DNA of eukaryotes is held within its nucleus. The organelles of eukaryotes allow them to exhibit much higher levels of intracellular division of labor than is possible in prokaryotic cells.

Figure: Comparing the sizes of a virus, a bacterium, and a eukaryotic cell

Additional differences between prokaryotes & eukaryotes:

Size Eukaryotic cells are, on average, ten times the size of

prokaryotic cells.

Genomic composition and length The DNA of eukaryotes is much more complex and therefore

much more extensive than the DNA of prokaryotes.

Cell Wall Prokaryotes have a cell wall composed of peptidoglycan, a

single large polymer of amino acids and sugar.Many types of eukaryotic cells also have cell walls, but none

made of peptidoglycan.

Turn to Geological Time Scale now…

GEOLOGICAL TIME SCALE

ERA PERIOD ABSOLUTE TIME (mybp) RELATIVE TIME*

----------------------------------------------------------------0------------------------------- 31 Dec midnightNeogene

CENOZOIC -------------------------------------24------------------------------ 30 Dec 1:00 amPaleogene

------------------------------------------------------------------------------65------------------------------- 26 Dec 6:00 pmCretaceous

---------------------------------144------------------------------- 20 Dec noonMESOZOIC Jurassic

--------------------------------213----------------------------- 14 Dec eveningTriassic

---------------------------------------------------------------------------248----------------------------- 11 Dec nightPermian

PALEOZOIC --------------------------------286----------------------------- 7 Dec eveningCarboniferous

---------------------------------360----------------------------- 2 Dec evening

History of the Earth

Devonian --------------------------------408----------------------------- 29 Nov nightSilurian --------------------------------438----------------------------- 26 Nov noonOrdovician -----------------------------------505----------------------------- 21 Nov midnightCambrian

------------------------------------------------------------------------590------------------------------ 14 Nov morningProterozoic

PRE - ----------------------------------------------------------------2500---------------------------- 11 JuneCAMBRIAN Archean ---------------------------- -------------------------------------------4500----------------------------- 1 Jan

* Relative time is an artificial compression of the Earth’s 4.5 billion year history into a single year to facilitate an understanding of the tremendous time periods involved since the Earth first formed.

Archean Era ~ Origin of Life

• Life appears about 3.5-4 bybp.

• Formation of continental land masses we know today.

• First fossils - small cells, bacteria like organisms

• Most interesting changes occurred in shallow marine habitat (many fossils preserved).

Figure A painting of early Earth showing volcanic activity and photosynthetic prokaryotes in dense mats

Archean/Proterozoic Era:

• Evidence of ancient prokaryotes found in S. Africa and W. Australia.

• Stromatolites = stroma ~ bed, lithos ~ rocks = banded domes of sedimentary rock similar to layered mats formed in salt marshes.

• Photosynthetic bacteria found in the layers.

Figure: Bacterial mats and stromatolites

Figure: Stromatolites in Northern Canada

Figure: Early (left) and modern (right) prokaryotes

Proterozoic Era:

• Oxygen precipitates out into the ocean via iron ore and from organisms’ metabolism.

• First Eukaryotes appear about 1.5 bybp.

• Ediacaran fauna =

• Early multicellular organisms, • ex., algae

• All fossils present are marine

• Mass extinction of Ediacaran fauna at end of this era.

Ediacaran fauna fossil

Figure: Spheroidal Gunflint Microfossils

Figure: Filamentous cyanobacteria from the Bitter Springs Chert

Early Paleozoic Era:

Cambrian Revolution:

• First Predators seen in fossil record.

• Crawling and swimming invertebrates.

• Mass extinction end of Cambrian, followed by radiation of many animals, such as:

– First vertebrates.

– Plants invade land along with fungi

– Another mass extinction

Middle Paleozoic Era:

• Radiation of fishes.

• First flightless insects.

• First seed plants and trees.

• Vertebrate animals invade land.

Late Paleozoic Era:

• Coal swamps form great coal deposits.

• Gymnosperm prominence.

• Reptile prominence.

• First flying insect radiation.

• First terrestrial food webs.

• Largest mass extinction in earth's history, about ONE million years long. – on average about 50% all species went

extinct.

Mesozoic Era:

• Dominant land animals radiate including,– dinosaurs, birds, flying reptiles, crocodilians

• Mammals appear on the scene.

• Angiosperm and insect radiation

– (2nd major radiation for insects).

• Major Cretaceous Extinction: Lost dinosaurs, linked to major cooling of earth, 65 MY ago

• How did we loose the dinosaurs?

Cenozoic Era:

• Mammalian radiation.– First large mammals appear.

– Mammals filled niches left empty by dinosaurs.

– Ecological Niche = reflects organisms biotic and abiotic needs.

– Antarctica and Australia break apart.

Figure The history of continental drift

Major Points of Earth's History:

• Long history of unicellular life, multicellular life arose relatively late, (early hot spot of activity, shallow marine habitat).

• Modern fauna and flora arose from number of extinctions and radiations over millions of yrs.

• Mass Extinctions follow similar pattern:– Associated with long periods of global cooling, followed

by periods of adaptive radiations based on new adaptive innovations, and the presence of unfilled niches.

Figure: Diversity of life and periods of mass extinction